Hypothyroidism is a clinical state of thyroid hormone deficiency that may have a primary or secondary (central) cause. Primary hypothyroidism, which is more common than secondary hypothyroidism, is defined as failure of the thyroid gland to respond appropriately to thyroid-stimulating hormone (TSH) produced in the anterior pituitary gland. Primary hypothyroidism can be caused by autoimmune disease (Hashimoto disease), iodine deficiency, or infiltrative diseases, or it can be caused iatrogenically by surgery or irradiation of the gland. Subclinical hypothyroidism refers to mildly increased TSH levels in the setting of normal thyroxine (T4) and triiodothyronine (T3) levels. Secondary hypothyroidism is defined as insufficient thyroid gland stimulation by the hypothalamus or pituitary gland.

What new information does this article provide?

This article provides a simple and concise review of the varied physical and neuropsychiatric presentations of hypothyroidism and important diagnostic and treatment information.

What are the implications for psychiatric practice?

Hypothyroidism presents with a myriad of neuropsychiatric signs and symptoms. It is therefore imperative that psychiatrists are aware of the varied presentations of hypothyroidism and the appropriate assessment of laboratory tests of thyroid function and the basic treatment options.

Drugs commonly associated with thyroid dysfunction include lithium and amiodarone. Lithium has an antithyroid effect that can cause hypothyroidism at any point in treatment, which may not reverse with discontinuation of the lithium. Valproate and carbamazepine have also been found to decrease T4 levels in patients treated long-term.1

The prevalence of hypothyroidism in the US general population is estimated to be 1 in 300 persons; however, rates of hypothyroidism are higher in certain populations.2 Hypothyroidism is 10 times more common in women than in men, but with increasing age, it becomes more common in persons of both sexes. Higher rates of hypothyroidism have been found in hospitalized patients in both medical and psychiatric settings than in the general public.3-5 Subclinical hypothyroid-ism is even more common and occurs in 4.3% to 8.5% of the general US population.2,6

Populations with a higher risk of hypothyroidism include postpartum women and persons with a family history, previous head or neck surgeries, endocrine conditions such as diabetes, and nonendocrine autoimmune disorders such as multiple sclerosis.

Signs and symptoms

The somatic signs and symptoms of hypothyroidism are varied and nonspecific (Table 1). A majority of these signs and symptoms may be linked to a decreased rate of metabolism and the accumulation of glucosaminoglycans associated with low levels of circulating thyroid hormones. Although the signs and symptoms of hypothyroidism are nonspecific, certain symptoms, such as cold intolerance, dry skin, constipation, muscle cramps, and fatigue, may have increased specificity for the disease.

The severity of the presenting complaints and physical findings usually reflects the degree of hypothyroidism. However, the presenting signs and symptoms of thyroid deficiency may vary with patient age and acuity of onset. Since the symptoms of hypothyroidism are nonspecific, many other illnesses can present with similar symptoms. The differential is broad, depending on the specific symptoms (Table 2).